Control circuit having excessive power load protection means



Aug. 1, 1967 CONTROL CIRCUIT R. E. MIERENDORF 3,334,286 HAVING EXCESSIVE POWER LOAD PROTECTION MEANS Filed June 15. 1964 l INVENTOR ROBERT E. MIERENDORF ATTORNEY C United States Patent 3,334,286 CONTROL CIRCUIT HAVING EXCESSIVE POWER LOAD PROTECTION MEANS Robert E. Mierendorf, Milwaukee, Wis., assignor, by

mesne assignments, to The Louis Allis Company, Milwaukee, Wis., a corporation of Delaware Filed June 15, 1964, Ser. No. 375,398 9 Claims. (Cl. 318-345) The present invention relates to control circuits, and more particularly .to control circuits for providing a controlling signal to electronic power circuitry associated with electromechanical apparatus and for protecting the electronic power circuitry from excessive powerloads. This invention may find application in a direct current drive having a DC. motor and an electronic power amplifier for controlling the armature voltage, and hence the speed, of the motor. A control circuit of the type described and claimed in this patent may be employed to provide a speed controlling signal to the power amplifier and to protect the electronic components contained therein from high power loads which otherwise would be encountered during certain operational sequences.

Control circuits are utilized to regulate the operation of electro-mechanical apparatus to desired operative conditions by providing a controlling signal to the power circuitry energizing the apparatus. To perform this function, the control circuit is provided with a reference signal corresponding to the desired operative conditions in the apparatus and a feedback signal from the apparatus corresponding to actual conditions in the apparatus. These two signals are compared by the control circuit, and the difference signal therebetween is applied by the control circuit to the power circuit of the apparatus and thence to the apparatus to change the conditions therein. The difference signal is applied by these circuits in a manner tending to reduce its magnitude; that is, to bring actual conditions in the apparatus into accord with desired conditions.

The power circuitry associated with the electromechanical apparatus is most commonly a high-gain amplifier. Thus, a small change in the reference-feedback difference signal input supplied by the control circuit to the power circuit will provide a power circuit, tending to correct immediately the discrepancy between dsired conditions and actual conditions in the apparatus. This prevents the difference signal from attaining significant size in most instances, as the control and power circuits constantly operate to reduce its magnitude. The high-gain amplifier power circuitry is, therefore, designed for operation with a small difference signal input.

However, dilference signals of considerable magnitude are encountered during apparatus operation in at least two situations. When the apparatus is started up, a large difference signal occurs, as there is a reference signal being supplied to the control circuit but no feedback signal since the apparatus is initially not operative. Also, when the reference signal is changed rapidly to call for different conditions in the apparatus, there is a large difference signal between the reference signal and the feedback signal until actual conditions in the apparatus again approach the desired ones.

These large difference signals will, of course, produce an extremely large output from the power circuitry because of the high-gain characteristics of the power circuit. In the past, rotary power supplies, such as rotary generators, have been employed to energize the electromechanical apparatus. These machines have a sufficiently large thermal time-constant to handle, without damage, the aforementioned high power outputs for the relatively short periods of time during which they occur. However, the development of improved electronic components, in particular semi-conductor transistors and rectifiers, has led to the increased use of these components in electro-mechanical apparatus power circuits. The thermal-time constants of semi-conductor elements are insufficient to handle extremely large power loads, even momentarily. Hence, the high power requirements imposed on the electronic elements of the power circuit during apparatus start-up or during rapid changes in the reference signal inevitably exceed the power handling capability of the electronic elements in the power circuitry, resulting in the activation of protective devices such as fuses, or damage and failure to the electronic elements.

The prior art has generally attempted to solve the problem of tection during a start-up of the apparatus, as these circuits require current feedback from the power circuit output to be operative. This is generally not available when the apparatus is where the reference signal is rapidly changed, time delays in the current feedback from the apparatus may prevent the current limit circuit from becoming operative in time to prevent damage to the electronic elements by the momentarily high power loads.

It is, threfore, an object of this invention to provide a control circuit for providing a control signal to electronic power circuitry associated with electro-mechanical apparatus and for protecting said electronic power circuitry from excessive power loads.

It is another object of this invention to provide a control circuit which is capable of providing a control signal to electronic power circuitry, which may be limited as to its maximum rate of change and value, to protect said electronic power circuitry from excessive power loads.

Yet another object of this invention is to provide a control circuit which may be adapted for use with a speed direct current drive comprising a DC. electronic high-gain and for protecting said power circuit from excessive power loads.

The control circuit described and claimed in this patent accomplishes the above objects by providing a signal to the electronic power circuitry which is proportional to the reference-feedback difference signal when the difference signal is small enough in magnitude not to endanger the power large difference signal, such as during start-up or rapid increases in the signal to the power circuit. This positive feedback process continues until conditions in the apparatus approach the desired conditions indicated by the reference signal or until another power limiting device, such as a current limit circuit, becomes operative.

Further advantages and features of the present invenstarted. Similarly, in the instance a tion relate to the particular arrangement and structure whereby the above identified and other objects of the invention are obtained. The invention, both as to its structure and mode of operation, will be better understood by reference to the following specification and drawing, forming a part thereof, wherein:

The single figure is a schematic diagram of the control circuit in accordance with the present invention.

Referring to the single figure, a control circuit in accordance with the present invention is indicated by the numeral 1. The associated electro-mechanical apparatus is shown as an adjustable speed direct current drive and is indicated by the numeral 3. This drive comprises direct current motor 5, positive armature voltage conductor 7, negative armature voltage conductor 9, and high-gain amplifier power circuit 11. Power circuit 11 is connected to alternating current supply lines through fuses 20. Power circuit 11 converts alternating current power from supply lines 10 to direct current by means of electronic elements such as semi-conductor controlled rectifiers 12. The amount of power supplied to D0. drive 3 by power circuit 11 is determined by the conduction intervals of controlled rectifiers 12, which are controlled by firing circuit 14. Firing circuit 14 is connected to the output of control circuit 1, appearing across output terminals 16 and 18, in a manner such that the power supplied to DC. drive 3 by power circuit 11 is proportional to the control signal provided to firing circuit 14 by control circuit 1. Motor field 13 is powered by field power circuit 15.

Control circuit 1 is energized by a power supply, shown illustratively as battery 17. This power supply may also be utilized to provide a reference signal corresponding to conditions desired in D0. drive 3 by employing potentiometer 19 and current limiting resistor 21. The reference signal from the wiper of potentiometer 19 is applied to the emitter-base terminals of transistor 31 as a positive signal tending to turn the transistor on. A feedback signal from DC. drive 3 is also applied to the base of transistor 31 from positive voltage conductor 25 through resistor 27, filter capacitor 29, current limit resistor 28, and rectifier 30. The feedback signal is proportional to the armature voltage existing in the DC. drive 3. If motor field 13 is constant, the armature voltage is proportional to speed, and hence may be used to regulate that condition. The feedback signal is a negative signal, in opposition to the reference signal from potentiometer 19, and tends to turn transistor 31 off. The difference signal between the above mentioned signals applied to the base of transistor 31 forms the input signal to control circuit 1.

The emitter-collector circuit of transistor 31 is connected across power supply 17 and in series with resistor 33. Resistor 33 is connected in parallel with a series circuit comprised of resistor 35, transistor 39, and resistor 37. More specifically, transistor 39 is connected in a common collector or emitter follower configuration, having resistor 35 in the base circuit and resistor 37 in the emitter circuit. Due to the high input impedance characteristics of a transistor in the emitter follower configuration, the major portion of the voltage produced across resistor 33 by the emitter-collector current of transistor 31 will appear across the input of transistor 39 and hence resistor 37. The voltage developed across resistor 37' appears at terminals 16 and 18, and serves as the output signal of control circuit 1 to power circuit 11. The collector of transistor 39 isconnected through resistor 40 to power supply 17.

Transistor 41 is connected in the common base mode, having the emitter connected to the positive armature conductor 25 through current limiting resistor 43, bias resistor 45, and filter capacitor 47. The collector of transistor 41 is connected to the collector of transistor 39, in shunt with resistor 40. The base of transistor 41 is connected to power supply 17.

A current limiting circuit includes sensing resistor 49 in the negative armature voltage conductor 9 of DC. drive 3. This resistor is connected in parallel with resistor 51 and capacitor 53. This parallel circuit is connected to the emitter-base circuit of transistor 55. The emitter-base circuit of transistor 55 also contains a current reference circuit comprised of a reference source, shown illustratively as battery 57, resistor 59, and potentiometer 61. The wiper of potentiometer 61 is connected to the base of transistor 55. The collector, or output, of transistor 55 is connected to the base of transistor 63 and resistor 69. The emitter of transistor 63 is connected to bias resistors 65 and 67. The collector of transistor 63 is connected to the base terminal of transistor 39.

As previously noted, control circuit 1 operates to provide a signal to power circuit 11, proportional to the difference signal between the reference signal and the feedback signal when said difference signal is so small as to not make dangerous power demands on the semi-conductor controlled rectifiers 12 of power circuit 11. When a large difference signal is applied to control circuit 1,

control circuit -1 provides a control signal which is limited both as to the maximum rate of change and as tovalue, to protect the electronic elements in power circuit 11. The operation of control circuit 1, first under conditions of small difference signals and then under conditions of large difference signals, is described in detail below.

When control circuit 1 and power circuit 11 are regulating conditions in DC. drive 3 to a constant value as determined by a constant reference signal, such control is generally accomplished by small difference signals. Thus, if the speed of DC. motor 5 varies, even slightly, from that demanded by the reference signal, the variance appears as a difference signal input to control circuit 1. That circuit supplies a signal to power circuit 11 in a manner to correct the variance. The high gain of power circuit 11 provides for prompt correction, preventing the diiference signal from getting too large.

The difference signal is applied to the base of transistor 31, resulting in a current flow from the collector of transistor 31 and the development of a voltage proportional to the diiference signal across resistor 33 in the collector circuit of transistor 31. The voltage across resistor 33 also appears across the parallel circut of resistor 35, the base-emitter circuit of transistor 39, and resistor 37, and serves as an input signal to transistor 39.

The emitter-collector circuit of transistor 39 is partially supplied with emitter-collector current from the emittercollector circuit of transistor 41. The emitter-collector current of transistor 41 is proportional to armature voltage conditions in DC. drive 3, as the emitter of transistor 41 is connected to conductor 25. Additional emitter-collector current for transistor 41 is provided by power supply 17 through resistor 40. The current through resistor 40 is proportional to the voltage across it, which is the difference between the voltage across resistor 37 in series with it and power supply voltage 17. The emitter-collector current of transistor 39 produces a voltage across resistor 37. This voltage is supplied to output terminals 16 and 18 as the output signal of control circuit 1. Transistor 39 uses only as much of the collector current available from the collector of transistor 41 and through resistor 40 as is demanded by the base-emitter signal to transistor 39. As the base-emitter signal to transistor 39 is proportional to the voltage across resistor 33, and therefore the difference signal applied to control circuit 1, the output signal of control circuit 1 will be proportional to the difference signal.

For example, if the armature voltage and'speed of DC. motor 5 decrease from the level sought to be established by the reference signal, the feedback signal decreases, increasing the difference signal between it and the reference signal. The increased difference signal is applied to the base of transistor 31, increasing the emittercollector current of transistor 31, the voltage across re- I of transistor 4 This increases the emitter-collector cur- 65 sister 33, and the base-emitter signal to transistor 39. The the output of control circuit 1, resulting in additional ingreater base-emitter signal increases the emitter-collector creases in the armature voltage and speed of DC. drive current of transistor 39 and hence the voltage across re- 3. This process cont nues at a rate determined by capacitor rent from transistor 41 1s decreased due to the decreased existing reduces the base-emitter current and hence armature voltage feedback there is sulficlent mltteremitter-collector current of transistor 39 and the output collector current available through resistor 40 to permit g or 111ml 3 Current feedback pp and the emitter-collector current increases by transistor 39 in rer n limiting Cir u t e mes Operative. sponse to base-emitter signal increases caused by small 10 The current limit circuit of control circuit 1 provides diiference signal increases The increased control $1 1181 additional protection to the semi-conductor controlled at terminals 16 and 18 increases the output of power fecfifiers 20 111 Power 11 byllmltlflg the maxlmum circuit 11 increasing armature voltage and bringing the Current that y pp In the armature clrcult A5 D speed of D C motor 5 up to the desired level viously noted current limiting circuitry alone is not sufii- Control circuit 1 operates in a similar but opposite eient for protection in instances of a large dilference sigmanner to reduce motor speed and armature voltage nal being applied to control circuit 1, since a current feedshould they increase in relation to the reference signal. back signal must be provided to the current limiting cir- Control circuit 1 operates in the following manner durcuitry before it will operate to reduce the current. By the ing start-up or rapid changes in the reference signal, to time the current limit circuit senses the increased armaprovideasignal to power circuit 11 which has acontrolled ture r the h r h m lc n of mi rate of increase and a limited maximum value The limited conductor rectlfiers 20 Wlll have been exceeded signal prevents the sudden surge of power through power e armature current in conductors 7 and 9 produces a circuit 11 WhlCll would otherwise occur due to the large voltage across resistor 49 in armature conductor 9 This difference signal present during these instances, from trigvoltage is filtered by resistor 51 and capacitor 53, and gering fuses 20 or damaging semi-conductor controlled produces an emitter-base current to transistor 55. This rectifiers 12. emitter-base current can flow only when the voltage across A large difference signal applied to the base of trancapacitor 53 is greater than the voltage on the wiper of sistor 31 results in maximum emitter-collector current potentiometer 61. The setting of potentiometer 61 confrom transistor 31, providing maximum voltage drop trols the value of armature current at which the current across resistor 33 and maximum base-emitter signal to limit circuit becomes effective, by preventing emitter-base transistor 39 This would ordinarily require maximum current flow in transistor 55 when the value of the armaemitter-collector current from transistor 39 and hence ture current, as expressed by the voltage across capac1tor maximum output signal from control circuit 1 53, is less than the maximum desired armature current limited in some manner, would produce a damagingly Transistor 55 controls the conduction state of tranmentioned, current lnnit circuits are ineffective to provide age across resistor 33 is applied to the base of transisa limitation under these circumstances because of time tor 39, and control circuit 1 operates 1n the above dedelays or the unavailability of current feedback. Control scribed manner When transistor 63 IS 111 the conducting circuit 1 provides the necessary limited control signal out- 40 state, a low impedance path is provided for the voltage put under these circumstances by limiting the emitteracross resistor 33, and the base-emitter signal is effectively collector current of transistor 39. The emitter-collector removed from transistor 39.

current of transistor 39 is limited to that available from When the armature current is below the maximum dethe parallel paths comprised of the emitter-collector cirsired value, transistor 63 is rendered non-conductive by curt of transistor 41 and resistor 40, regardless of the 45 the current flow through resistors 65 and 67, which makes magnitude of the base-emitter current to transistor 39. the emitter of transistor 63 more positive than the base us, upon a large increase in the dilference signal, the when there is no current through resistor 69 in the base emitter-collector current of transistor 39, and hence the circuit. There will be no cur as transistor 55 is rendered non-conductive by only to the amount available from the collector of tranthe voltage across potentiometer 61. With transistor 63 sistor 41 and through resistor 40 The maximum avallnon-conductive, the voltage across resistor 33 is applied able emitter-collector current from transistor 39 provides to the base terminal of transistor 39, and control circuit 1 for an initial moderate increase in the output of control functions in the normal manner. When, however the voltcontrol circuit 1, allowing D.C. drive 3 to attain the speed Wiper of potentiometer 61 i overcomes the bias on transistor 63 produced by the curcuit 11 and the armature voltage and speed of DC. rent flow through resistors 65 and 67, transistor 63 is rendrive 3. The increase in armature voltage is fed back to dere control circuit 1 through conductor 25. The increased from transistor 39. This red armature voltage is filtered and delayed by resistor 43 and rent of transistor 39, capacitor 47, and applied to the emitter-collector circuit across resistor 37 an rent of transistor 41. The increased emitter-collector curcurrent.

rent of transistor 41 results in a greater current in the Thus, the above described control circuit provides for i and hence a both the control of conditions in electro-mechanical apgreater voltage across resistor 37 and output signal from paratus, by providing a power controlling signal to the control circuit 1. The greater signal from control circuit power circuitry responsible for conditions in the appara- 1 produces a larger output from power circuit 11 and an tus; and for th damage due to large power loads, by limiting the conincrease in the armature voltage produces increases in described above is at present thought to be preferred, it will be appreciated that modification or alternation may be made therein without departing from the spirit of the invention, and it is intended to include all such modifications as come within the scope of the claims below.

What is claimed is:

1. A control circuit producing a control signal to an electronic power "circuit for regulating associated electromechanical apparatus in accordance with the difference signal between a reference signal and a feedback signal and for protecting said power circuit during periods of a large difference signal comprising:

a power supply;

a reference signal source connected to said power supply producing a reference signal corresponding to desired conditions in the apparatus;

means producing a negative feedback signal corresponding to conditions existing in the apparatus;

first transistor means having an input connected to said reference signal source and said means producing a feedback signal and sensitive to the difference signal between the reference signal and the feedback signal and producing an output proportional to said difference signal;

second transistor means connected across said power supply and receiving a limited power signal therefrom, said transistor having an input connected to the output of said first transistor means and an output providing a control signal to the power circuit; and

third transistor means connected to the apparatus and to said second transistor means to supply a positive feedback signal from said apparatus to said second transistor means as a power signal;

whereby the control circuit produces a control signal to the power circuit proportional to the signals supplied to said second transistor means by said power supply and said third transistor means under conditions of a large difference signal between the reference signal and the feedback signal and proportional to the difference signal between the reference signal and the feedback signal under other conditions.

2. A control circuit producing a control signal to an electronic power circuit for regulating associated electromechanical apparatus in accordance with the difference signal between a reference signal and a feedback signal and for protecting said power circuit during periods of a large difference signal comprising:

a power supply;

a reference signal source connected to said power supply producing a reference signal corresponding to desired conditions in the apparatus;

means producing a negative feedback signal corresponding to conditions existing in the apparatus;

first transistor means having an input connected to said reference signal source and said means producing a feedback signal and sensitive to the difference signal between the reference signal and the feedback signal and producing an output proportional to said difference signal;

second transistor means connected across said power supply and receiving a limited power signal therefrom, said transistor having an input connected to the output of said first transistor means and an output providing a control signal to the power circuit;

third transistor means connected to said [apparatus and to said second transistor means to supply a positive feedback signal from said apparatus to said second transistor means as a power signal; and

means connected to said second transistor means forming a bypass for the input to said second transistor means to reduce said control signal to the power circuit during extended periods of large difference signal;

whereby said control circuit produces a control signal to the power circuit proportional to the signals supplied to said second transistor means by said power supply and said third transistor means until said bypass means reduces said control signal under conditions of a large difference signal between the reference signal and the feedback signal and proportional to the difference signal under other conditions.

3. A control circuit producing a control signal to an electronic power circuit for regulating associated electro-mechanical apparatus in accordance with the difference signal between a reference signal and a feedback signal and for protecting said power circuit during periods of a large difference signal comprising:

a power supply;

a reference signal source connected to said power supply producing a reference signal corresponding to desired conditions in the apparatus;

means producing a negative feedback signal corresponding to conditions existing in the apparatus;

first transistor means having an input connected to said reference signal source and said means produring a feedback signal and sensitive to the difference signal between the reference signal and the feedback signal and producing an output proportional to said difference signal;

second transistor means connected across said power supply and receiving a limited power signal therefrom, said transistor having an input connected to the output of said first transistor means and an output providing a control signal to the power circuit;

third transistor means connected to the apparatus and to said second transistor means to supply a positive feedback signal from the apparatus to said second transistor means as a power signal;

a first signal means connected to the apparatus sensing the effect of large difference signals in the apparatus and producing a signal corresponding to said effect;

a second signal means producing a signal corresponding to the maximum desired effect of large difference signals in the apparatus;

fourth transistor means connected to said first signal means and said second signal means capable of being turned on when the signal from said first signal means exceeds the sign-a1 from said second signal means; and

fifth transistor means connected to said fourth transistor means and to said second transistor means capable of being turned on when said fourth transistor means is in the conducting state to bypass said input signal from said second transistor means and reduce the control signal to the power circuit;

whereby the control circuit produces a control signal to the power circuit proportional to the signal supplied to said second transistor means by said power supply and said third transistor means until said fifth transistor means bypasses said input to said second transistor means under conditions of a large difference signal and proportional to the difference signal under other conditions.

4. A control circuit producing a control signal to an electronic power circuit for regulating associated electromechanical apparatus in accordance with the difference signal between a reference signal and a feedback signal and for protecting said power circuit during periods of a large difference signal comprising:

a power supply;

a reference signal source connected to said power supply producing a reference signal corresponding to desired conditions in the apparatus;

means producing a negative feedback signal corresponding to conditions existing in the apparatus;

first transistor means having an emitter, a collector, and a base, said reference signal source and said means producing a feedback signal connected to said base to produce an input signal corresponding to the difference between the reference signal and the feedr 10 back signal, said emitter and collector connected said control signal under conditions of a large difierence across said power supply and in series with a resignal and proportional to the difference signal under sistor; other conditions. second transistor means having .an emitter, a collec- 6. The control circuit of claim wherein said means tor, and a base, eorine ted i parallel with said re- 5 connected to the apparatus and said second transistor si to and d ri in ba e-e itt cu rent th refrom, means sensitive to the effect of large difference signals in said collector co ct d t aid power supply t the apparatus and forming a bypass for the base-emitter provide limited itt ll t u t to id current of said second transistor means to reduce the conond tr sist means; trol signal to the power circuit comprises: means in the emitter circuit of said second transistor first gn l means Connected to the apparatus sensing mean furni hi a t l signal t th power i the eflect of arge difference signals in the apparatus cuit in accordance with the emitter-collector curand Producing a Signal Corresponding thereto; rent of said second transistor means; and Second signal means producing a signal corresponding third transistor means having an emitter, a collector, the maximum desired etfect of large difierehee and a base, said base connected to said power supply, slgnals in the pp the emitter-collector circuit of said third transistor fourth transistor means Connected to said fi t signal means connected to said apparatus and the collector {heahs and Said Second Signal means, Capable f of said second transistor means to provide a positive 111g turned on When the Signal from sa1d first Signal feedback emitter-collector current proportional to means eXeeeds the Signal from Said Second Signal conditions in the apparatus; means; whereby said control circuit produces a control signal h trahslstor means connected to a f rth tranproportional to the emitter-collector current supplied to slstor means f to Said Second t ns s r means second transistor means by said third transistor means a e of being turned on n aid fourth tranand i power Supply under conditions f large difsistor is turned on, to bypass the base-emitter current ference signal between the reference and feedback signals from salfi Second translstor'mefms and reduce e and a control signal proportional to the difference signal control slghal to the Power clreultbetween the reference and feedback signals under other afilrect current drive having E1 motor, n aconditl-Ons. ture circuit and a variable armature power circuit for 5 A 1 circuit producing a Control Signal to an controlling the speed of said motor, a control circuit proelectronic power circuit for regulating associated electro- Vldmg a Speed cohtrolhhg slghai t0 831d P r l ult 1n mechanical apparatus in accordance with the difference accordance'wlth a l'eferehee'feedhaek difference ignal signal between a reference signal and a feedback signal and Pr 9tect1oh sald P K circuit during p i ds f a and for protecting said power circuit during periods of large dlfference slgnal Comprising: a large difference signal comprising: a Power PR Y;

a Power Supply; I a reference signal source connected to said power supa reference signal source connected to said power sup- P a referehee Signal p nding to ply producing a reference signal corresponding to desired conditions in said direct current drive; desired conditions in the apparatus; mtfans producfhg a h t tedback Signal p means producing a negative feedback signal corremg to Qondltlons 111 said dlreet Current rive;

Spending to conditions in the apparatus; 40 first transistor means having an emitter, a collector, first transistor means having an emitter, a collector, and a base Sald reference Signal Source and said and a base, said reference slgnal source and said means producing a feedback signal connected to said means producing a feedback signal connected to said b ase to Produce an Input Signal r p n ing 0 the base to produce an Input slgnal correspondmg to the difference between the reference signal and the feeddifference between the reference signal and the feed- 5 back slgnah sald emitter and Collector Connected back signal said emitter and collector connected across Sald Power pp y and n se ies with a reacross the power supply and in series with a reslstor; sistor; second transistor means having an emitter, a collector, second transistor means having an emitter, a collector, and a e connected in Parallel With a resistor and a base, connected in parallel with said resistor and derlvlh'g base-emitter Current th refr m, said and deriving base-emitter current therefrom, said cPllector )nnected to Said Power pp y to P V de collector Connected to Sal-d power supply to provide l mited emitter-collector current to said second tranlimited emitter-collector current to said second trans1Str means; Sister means; means in the emitter circuit of said second transistor a resistor in the emitter circuit of said second tranj furmshlng a h Signal to the P r C rsistor means furnishing a control signal to the power cult accordance Wlth the emitter-Collector Curcircuit in accordance with the emitter-collector current of t Second transistor means; and rent of said second transistor means; thlrd translstor fneahs having an emitter, a Collector, third transistor means having an emitter, a collector, and a blaser Sald base @nne'cted to said Power p y and a base, Said base connected to Said power supply the emitter-collector circuit of said third transistor the emitter-collector circuit of said third transistor means Connected to the armature circuit and t0 a means Connected to the apparatus and to Sald COL collector of said second transistor means to provide lector of Said Second transistor means to provide a a posit ve feedback em tter-collector current thereto; positive feedback emittepcouector current thereto; whereby said control circuit produces a control signal and proportional to the emitter-collecor current provided to means connected to the apparatus and said second tran- ,sald Second transistor means and sald POWer pp y u sistor means sensitive to the effect of large difference mg condltlons of a large inference slgnal between the slgnals m the apparatus and fol-Hung a bypass for reference and the feedback signals and an output signal the base emltter current of sald Second translstor proportional to the difference signal between the reference means under conditions of a large diff Signal signal and the feedback signal under other conditions. to reduce the control signal to the power circuit; In a direct current time having a at1 armawhereby the control circuit produces a control signal prou elreult and a Va ia e a ma ure power circuit for gortional to the emitter-collector current supplied to said c ntrolling the speed of said motor a control circuit econd transistor means by said third transistor means providing a speed controlling signal to said power circuit and said power supply until said bypass means reduces in accordance with a reference-feedb 1 1 l 2 and protection to said power circuit during periods of a said second transistor means by said third transistor large difference signal comprising: means and said power supply until said means sensitive a power supply; to overload conditions reduces said control signal under a reference signal source connected to said power supconditions of a large difference signal and proportional ply producing a reference signal corresponding to 5 to the difference between the reference signal and the desired conditions in said direct current drive; feedback signal under other conditions.

means producing a negative feedback signal corre- 9. The control circuit of claim 8 wherein the means sponding to conditions in said direct current drive; connected to the armature circuit and to said second tranfirst transistor means having an emitter, a collector, and sistor means sensitive to overload conditions in the armaa base, said reference signal source and said means 10 ture circuit and forming a bypass for said base-emitter producing a feedback signal connected to said base current to said second transistor means under such conto produce an input signal corresponding to the difditions to reduce the control signal to the power circuit ference between the reference signal and the feedcomprises:

back signal, said emitter and collector connected first signal means connected to the armature circuit across said power supply and in series with a resissensing overload conditions in the armature circuit tor; and producing a signal corresponding thereto;

a second transistor having an emitter, a collector, and second signal means producing a signal corresponding a base, connected in parallel with said resistor and to maximum desired overload conditions in the deriving base-emitter current therefrom, said 001- armature circuit; lector connected to said power supply to provide fourth transistor means connected to said first signal limited emitter-collector current to said second tranmeans and said second signal means, capable of sistor means; being turned on when said signal from said first a resistor in the emitter circuit of said second transissignal means exceeds the signal from said second sigtor means furnishing a control signal to the power nal means; and circuit in accordance with the emitter-collector curfifth transistor means connected to said fourth tranrent of the second transistor means; sistor means and to said second transistor means third transistor means having an emitter, a collector, capable of being turned on when said fourth tranand a base, said base connected to said power supsistor means is turned on, to bypass the base-emitter ply, the emitter-collector circuit of said third trancurrent from said second transistor means and reduce sistor means connected to the armature circuit and the control signal to the power circuit. to said collect-or of said second transistor means to provide a positive feedback emitter-collector cur- References Cited rent thereto; and

means connected to the armature circuit and said sec- UNITED STATES PATENTS ond transistor means sensitive to overload conditions 3,037,157 5/1962 Young 3l8-317 X in the armature circuit caused by a large difference 3,124,698 3/ 1964 Semmer et al. signal and forming a bypass for the emitter-base cur- 3,249,840 5/ 1966 Erikson 318-345 X rent to said second transistor means under such 3,262,015 7/1966 M N et 1 conditions to reduce the control signal to the armature power circuit;

whereby said control circuit produces a control signal ORIS RADERPrimary Examiner proportional to the emitter-collector current supplied to J. C. BERENZWEIG, J. J. BAKER, Assistant Examiners. 

1. A CONTROL CIRCUIT PRODUCING A CONTROL SIGNAL TO AN ELECTRONIC POWER CIRCUIT FOR REGULATING ASSOCIATED ELECTROMECHANICAL APPARATUS IN ACCORDANCE WITH THE DIFFERENCE SIGNAL BETWEEN A REFERENCE SIGNAL AND A FEEDBACK SIGNAL AND FOR PROTECTING SAID POWER CIRCUIT DURING PERIODS OF A LARGE DIFFERENCE SIGNAL COMPRISING: A POWER SUPPLY; A REFERENCE SIGNAL SOURCE CONNECTED TO SAID POWER SUPPLY PRODUCING A REFERENCE SIGNAL CORRESPONDING TO DESIRED CONDITIONS IN THE APPARATUS; MEANS PRODUCING A NEGATIVE FEEDBACK SIGNAL CORRESPONDING TO CONDITIONS EXISTING IN THE APPARATUS; FIRST TRANSISTOR MEANS HAVING AN INPUT CONNECTED TO SAID REFERENCE SIGNAL SOURCE AND SAID MEANS PRODUCING A FEEDBACK SIGNAL AND SENSITIVE TO THE DIFFERENCE SIGNAL BETWEEN THE REFERENCE SIGNAL AND THE FEEDBACK SIGNAL AND PRODUCING AN OUTPUT PROPORTIONAL TO SAID DIFFERENCE SIGNAL; 